Thermal relay for fluorescent lamps



Dec. 31, 1946.

mumr/o H.-J. M CARTHY THERMAL RELAY FOR FLUORESCENT LAMPS Original Filed Sept. 12, 1940 I Patented Dec. 31, 1943 2,413,363 I THERMAL RELAY FOR FLUORESCENT LAMPS Henry J. McCarthy, Danvers,

Sylvania Electric Products, Inc., Salem,

Mass., assignor to Mass.,

a corporation of Massachusetts Continuation of application Serial No. September 12, 1940. This application 1943, Serial No. 471,200

356,566, January 2 Claims- (Cl. 200122) V v i.

This invention refers to electric gaseous discharge lamps and in particular to'thermal relays for operating fluorescent lamps. This application is a continuation of my co pending application Serial No. 356,566, filed September 12, 1940.

An object of this invention is to provide a starting switch for electric gaseous discharge lamps which will permit the cathodes of the lamp to be plileheated before the discharge is started between t em.

Another object is to provide a starting switch which will be so timed in its action that no greater interval of time the cathode than is absolutely necessary.

A further object is to provide a switch which will function under all possible conditions of starting and restarting,

will elapse for the preheating of Another object is to provide a switch which will be so mounted as to be capable of withstanding accidental, careless or rough usage without having the precisely adjusted parts thrown out of alignment.

A feature of this starting apparatus is that it eliminates the unnecessary time lag present in many switches during the starting and restartlng period.

Another feature of this switch is that it is so mounted that even if it were dropped or otherwise mishandled, the precisely adjusted parts would not be disturbed.

Other objects, advantages and features will be apparent from the following specifications taken in conjunction with the accompanying drawing in which:

Figure 1 isa front relay assembly.

Figure 2 is a side elevation detail of the thermal relay.

Figure 3 is, a front below of the thermal relay assembly with the container partly cut away to show the insulating means.

Figure 4 is a schematic wiring diagram of the thermal relay. l I

Similar reference characters refer to similar parts in the several views of the drawing and in the specifications which follow.

The switch in my invention comprises a condenser. a resistance rod supported between and connected to the two lead-in wires, a bimetallic perspective of the thermal perspective viewed from I strip bent around the resistance rod, and a high and twolowresistance polnts..

The condenser I is mounted on the mounting plate 2, having its. lead-in wires 3- extending thrpughthe eyelets 4. The resistance rod 8, sup- .eyelets and the base plate l0, respectively, any other ported between and connected to the lead-in wires l and t, is also mounted on the mounting plate 2 but on the side opposite the condenser E. The lead -in wires l and ii of the resistance rod 3 are joined to the lead-in wires 3 of the condenser at'the eyelets d. The joining of these two sets of lead-in wires at the eyelets 6 may be done by spot-welding, soldering or somesimilar means. The lead-in wires 3 of the condenser l are projected through the eyelets 4% in thernounting plate 2 and extend down through the eyelets 9 in the circular base plate ill and into the base pins 5 where they may be soldered. Although 4 and 9 are used in the mounting plate 2 material may be used that will permit a joining and fixing of the lead-in wires at these points. Eyelets, or some similar means are necessary due to the fact that the base plate and mounting plate are made of Bakelite or some similar insulating material.

p The supporting arm ll of nickel or some similar material extends inwardly from the lead-in wire 71, and attached to the inward end thereof is the bimetallic strip it? which is bent around the resistance rod 6. Attached to the inner side of the free end of the bimetallic strip l? is the low resistance contact 25. The resistance rod may have thereon an insulating coating ill of, for example, alumina and shellac.

I have found that an insulating coating of alumina and shellac is best suited for the particular purpose for which it is herein employed. 2 apply two coats of a dewaxed shellac and then two coats of an alumina-shellac mixture. Each coat isbake'd before another coat is applied. Al-

though I have used two coats of shellac and two coats of alumina and shellac the number of coats may be varied inasmuch as uniformity of the coating is the object to be attained. I have just applied two coats of shellac before applying any alumina because with the shellac foundation a higher breakdown voltage is obtained. This coating also prevents the bimetallic strip irom cut ting through the resistance rod.

The supporting arm I4 of nickel or some slmlend of the u shaped arm-is the low resistance contact l8, which may be of silver and which is normally open in respect to the bimetallic strip tact between the plates, but not a connection.

l2. This low resistance contact acts as an aux-- iliary starting means for if the filaments of the lamp have not been sufficiently heated to start the discharge across the lamp, by the time the bimetallic strip breaks away from the high resistance contact H, the current in the resistance rod 6 will continue to heat the bimetallic strip l2 and cause the strip l2 to bend back causing the low resistance contact 25 attached thereto, to touch the low resistance contact l8 thus shortcircuiting the resistance rod and starting the preheating of the lamp filaments.

The lead wires 3 cushion am! shock received by the base I!) and are rigid enough to act as supports and yet resilient enough'to provide cushioning action for the plate 2 and the various members mounted thereon. I

The entire switch unit may be inserted in a metal container l9 and may be insulated therefrom by a thin tube of insulating paper 22 The resistance rod should have a high resistance, say 40,000 ohms. For this resistance I have long and 0.65 inch in diameter. For my high resistance contact I have used carbon, having a contact resistance of about to ohms. For

my low resistance contacts I have used silver,

having a resistance of a fractional part of an ohm. Although I have used these particular materials, my invention does not necessitate the use of these exact same materials. It' is sufiicient that a high resistance contact point, low resistance contact points and a high resistance rod be used. A condenser of .006 microfarad across the contacts has proven to be advantageous for the elimination of radio interference.

The mounting plate 2 is not mounted flush on the base plate I0,-,but is so cut as to be elevated from the base plate at the points-where the condenser lead-in wires 3 extend down into the base pins 5. If this were not done it would be quite difficult to centrally locate the mounting plate used, for example, a resistance rod, 0.45 inch 2 on the base plate In and still have the wires 3 extending down into the base pins in their pro er positions. The base pins may be of the type suitable for use in a socket of the type described in Patent #2,261,170, in my name, and datedNovember 4, 1941.

The manner in which this switch is mounted allows for considerable accidental misuse. Due

to the fact that several of the parts which are,

vital tothe operation of the switch are very finely proportioned and the slightest change therein would cause inefiective or ineflicient operation,

this switch is mounted in a manner asto have 1 those parts which are not finely proportioned backward, the shock being entirely absorbed by i the flexible lead-in wires of the condenser.

The mounting plate 2 may rest on the base plate 1 although it is preferably held in spaced relation therewith. The only connection between around the-inner wallof the container l9 and a wafer 21 of insulating material in the top of the container. This container may have several tangs 20, on the open end which may extend over the base plate l0 after the switch has been inserted in the container. The base plate I0 has several notches 2|, therein, over which the tangs 20 are bent. If these tangs 2!] ever became loose and permitted the base plate to move, the switch would not be affected, for the movement of the switch would be absorbed by the flexible wires 3 of the condenser, thereby protecting the more sensitive and vital parts of the switch and preventing them from being thrown out of alignment.

The contour of the mounting plate may take any desired shape. The contour, as shown in Figure 1, has been selected because it facilitates and makes easier the welding operations on the.

thermal relay. The contour of the sides of the base pins may be flat or grooved depending on the type of contacts used. If a wire contact is used, I have found that pins with grooved sides provide a firmer contact surface.

What I claim is:

1. A thermal relay unit for electric discharge lamps comprising a horizontal rigid base plate of insulating material, arigid thermal switch supporting plate of insulating material perpendicular to said base plate, a U-shaped conductor member of relatively stiff wire disposed in substantially parallel spaced relation to said plate and having a high resistance portion in the portion between its side sections, rigid anchoring means for securing the free ends of said conductor member to said thermal switch supporting plate; a bimetallic member in close proximity to said resistance portion, a supporting arm fixed to one of the side sections of said conductor acting to support said bimetallic member, a contact member adjacent the free end of said bimetallic member, a supporting arm fixed to the other side section of the conductor member acting to support said contact member, a pair of contact pins fixed in said base plate and semi-flexible lead wires connected to the points of attachment of the conductor member with said vertical plate acting flexibly to support said vertical plate and the thermal switch thereon from said base plate. 2. A thermal relay unit for electric discharge lamps having the elements defined in claim 1 and in which the said vertical supporting plate is I-beam shaped in outline.

HENRY J. McCARTI-IY. 

